The long-term objectives of this project are to use the data of comparative neuroanatomy, neurophysiology and neuropsychology to: (1) reconstruct the evolutionary history of the visual system; and (2) understand the relationship between structure and function within the visual system. The rationale for studying visual information processing in the nervous systems of non-mammalian vertebrates is that by understanding the general mechanisms of such processing, common to all amniotes (and perhaps all vertebrates), we may gain insights in the mechanisms of vision in humans that might not otherwise be available from experiments limited to the traditional subjects of such research, i.e., rats, cats and monkeys. The subjects of this research are pigeons, because these birds are highly specialized for vision. In this renewal application, we are proposing to continue our anatomical investigations of the cell populations that comprise the avian visual system and to continue to use the techniques of animal psychophysics and sensory scaling to describe the effects of selective lesions in these cell groups. The broad goal is to unravel the mechanisms of deficit and sparing after visual system injury by using behavioral tests of sensory capacty, attention, perception and information processing and relating these data to the anatomy and physiology of the visual system.